1. If a victim testifies on sentencing–the rules of evidence apply the same as any other witness. Article 6b does not waive the rules of evidence when a victim testifies in sentencing. (Note, the victim gave both sworn and unsworn statements.) Failure to follow the rules (even without defense objection) gets the defense and government, and court to agree there was an error and to get a new sentencing hearing.
2. It is NEVER EVER a good idea for an accused (or one of his witnesses) to impeach the verdict. Gone are the days when we could legally seek reconsideration of the findings, even through sentencing. The legitimate tactic at the time was to present the accused’s version of events through his unsworn and then argue that the members may wish to reconsider the findings.